April 27, 2011

This figure shows the Agulhas system and its leakage into the South Atlantic. The southward shift of the winds in a warming climate (right panel) cause a southward shift of the subtropical front (red arrows), enlarging the "gateway" for Agulhas leakage around the tip of Africa. Increased Agulhas leakage acts to enhance Atlantic overturning, which causes a feedback on climate. (Background colors are dynamic height integrated between 2000 m and the surface). Credit: Erik van Sebille, UM/RSMAS

(PhysOrg.com) -- The Agulhas Current which runs along the east coast of Africa may not be as well known as its counterpart in the Atlantic, the Gulf Stream. But now researchers are taking a closer look at this current and its "leakage" from the Indian Ocean into the Atlantic Ocean--and what that may mean for climate change.

In results of a study published in this week's issue of the journal Nature, a team of scientists led by University of Miami Rosenstiel School of Marine & Atmospheric Science Oceanographer Lisa Beal, suggests that Agulhas leakage could be a significant player in global climate variability.

The Agulhas Current transports warm and salty waters from the tropical Indian Ocean to the southern tip of Africa. There most of the water loops around to remain in the Indian Ocean (the Agulhas Retroflection), while some water leaks into the fresher Atlantic Ocean via giant Agulhas rings.

Once in the Atlantic, the salty Agulhas leakage waters eventually flow into the Northern Hemisphere and act to strengthen the Atlantic overturning circulation by enhancing deep-water formation.

Atlantic overturning circulation is technically known as Atlantic meridional overturning circulation (AMOC); it carries warm shallow water into northern latitudes and returns cold deep water southward across the equator.

Recent research points to an increase in Agulhas leakage over the last few decades, caused primarily by human-induced climate change.

The finding is profound, oceanographers say, because it suggests that increased Agulhas leakage could trigger a strengthening in Atlantic overturning circulation--at a time when warming and accelerated meltwater input in the North Atlantic has been predicted to weaken it.

"This could mean that current IPCC model predictions for the next century are wrong, and there will be no cooling in the North Atlantic to partially offset the effects of global climate change over North America and Europe," said Beal.

Current meters are secured to lab benches, ready for deployment into the Agulhas Current. Credit: Lisa Beal

There are also paleoceanographic data to suggest that dramatic peaks in Agulhas leakage over the past 500,000 years may have triggered the end of glacial cycles.

These data are further evidence that the Agulhas system and its leakage play an important role in the planet's climate, Beal and others say.

"This study shows that local changes in atmospheric and oceanic conditions in the Southern Hemisphere can affect the strength of the ocean circulation in unexpected ways," said Eric Itsweire, director of the National Science Foundation (NSF)'s physical oceanography program, which funded the research.

"Under a warming climate," said Itsweire, "the Agulhas Current system near the tip of South Africa could bring more warm salty water from the Indian to the Atlantic Ocean and counteract opposing effects from the Arctic Ocean."

The study establishes the need for additional research in the region that focuses on Agulhas rings, as well as on the leakage, believes Beal.

Climate modeling experiments are critical, she said, and need to be supported by paleoceanographic data and sustained observations to firmly establish the role of the Agulhas system in a warming climate.

A current meter and chain of floats are deployed as part of several-kilometers-long mooring. Credit: Lisa Beal

"Our goal now is to get more of the scientific community involved in research on the Agulhas system and its global effects," said Beal. "The emphasis has been too long in the North Atlantic."

The Agulhas Current Time-Series Experiment, or ACT, was launched in April 2010 to measure the variability of the Agulhas Current using a combination of current meter moorings and satellite data.

Beal, who serves as chief scientist, spent one month aboard the research vessel Knorr in the southwest Indian Ocean deploying oceanographic instruments.

The data gathered in situ, when combined with along-track satellite information, will help increase our understanding of how the Agulhas system is changing in a warming climate, Beal said.

The scientific team included Beal, Wilhelmus P.M. de Ruijter of Utrecht University in the Netherlands, Arne Biastoch of Leibniz- Institut für Meereswissenschaften (IFM-GEOMAR) in Germany, and Rainer Zahn of the Universitat Autònoma de Barcelona in Spain.

It also included members of the Scientific Committee for Oceanic Research (SCOR) Working Group 136 on the Climatic Importance of the Agulhas System, sponsored by SCOR, the International Association for the Physical Sciences of the Oceans, and the World Climate Research Program.

Monitoring the saltiness of the ocean water could provide an early indicator of climate change. Significant increases or decreases in salt in key areas could forewarn of climate change in 10 to 20 years time. Presenting their ...

The senior science advisor to the World Climate Research Programme (WCRP) has called for the establishment of a Southern Hemisphere network of deep ocean moorings to detect any change in ocean circulation that may adversely ...

Very large and abrupt changes in temperature recorded over Greenland and across the North Atlantic during the last Ice Age were actually global in extent, according to an international team of researchers led by Cardiff University.

The PhD project presented by Gema Martínez-Méndez from the Institute of Environmental Science and Technology at the Universitat Autonoma de Barcelona focuses on the Agulhas Current and the ensuing warm water ...

An international team of investigators under the leadership of two researchers from the UAB demonstrates the response of the Atlantic Ocean circulation to climate change in the past. Global warming today could have similar ...

Recommended for you

At the end of the Pleistocene period, approximately 12,800 years ago—give or take a few centuries—a cosmic impact triggered an abrupt cooling episode that earth scientists refer to as the Younger Dryas.

In a new assessment of nine state-of-the-art climate model simulations provided by major international modeling centers, Michael Rawlins at the University of Massachusetts Amherst and colleagues found broad disagreement in ...

New research confirms that the land under the Chesapeake Bay is sinking rapidly and projects that Washington, D.C., could drop by six or more inches in the next century—adding to the problems of sea-level rise.

The world's deserts may be storing some of the climate-changing carbon dioxide emitted by human activities, a new study suggests. Massive aquifers underneath deserts could hold more carbon than all the plants on land, according ...

Wildfires in California's fabled Sierra Nevada mountain range are increasingly burning high-elevation forests, which historically have seldom burned, reports a team of researchers led by the John Muir Institute of the Environment ...

The above abstract indicates to me that the research noted indicates that the AMOC will increase heat distribution resulting in a warmer polar system and lesser warming at the equator when compared to the previously discussed models of the AR4. This could be construed as positive or negative, dependant on your stance on currently understood AGCC research.

It does mean that current climate models, as used by the IPCC, may underestimate warming at higher Northern latitudes.

If this finding pans out, it might explain some features of recent glacial - interglacial transitions, such as why despite considerable amounts of fresh water being added to the AMOC (because of land-ice melt), these transitions tend to proceed so quickly.

let us recall the outstanding success of financial model from 2000 to 2008. even with a great deal more data it was catastrophic. aerodynamically bumble bee are incapable of flight. extrapolation is a very dangerous to reality

let us recall the outstanding success of financial model from 2000 to 2008. even with a great deal more data it was catastrophic. aerodynamically bumble bees are incapable of flight.

You are exactly right.

Output from even the most expensive computer is no more valid than the input data and the models programmed into the computer.

I personally knew that the input data on Earth's heat source [1] was seriously flawed, and Earth's changing climate has since demonstrated errors in the climate predictions of Al Gore, the UN's IPCC and the alliance of world leaders.